In Mexico, according to NOM-086-SENER-SEMARNAT SCFI-2005, the content of total sulphur in Diesel should be reduced up to 15 ppm in weight, this implies the production of ultra low sulphur diesel, for which PEMEX has carried out significant modifications in the HDS process and all of the catalysts used to produce Diesel Ultra low sulphur (DUBA) are currently imported.
The elimination of sulphur and nitrogen compounds from fossil fuels is a priority in recent years. Sulfur and nitrogen compounds present in hydrocarbons when subjected to the combustion process, gas emissions like SOx and NOx are produced which are highly toxic and are the main promoters of acid rain.
The alternative used in the oil industry to remove these contaminants is the process of hydrodesulfurization (HDS), consisting in a reduction reaction at high pressures and temperatures of the sulfur and nitrogen components in the presence of hydrogen using catalysts. This process is extremely expensive, and although aliphatic sulfur and nitrogen compounds are reduced, it is inefficient in the reduction of aromatic compounds.
Different non-conventional alternatives to remove sulphur and nitrogen compounds have been studied. An alternative is the use of ionic liquids for the selective removal of these compounds through a process of liquid-liquid extraction.
Mexican heavy crudes are characterized by a high content of nitrogen compounds, which in addition to generate toxic gases, they are important inhibitors of the HDS reaction, so the prior removal of nitrogenous compounds contributes to achieve the sulphur levels required in less severe operating conditions and increase the life time of the catalysts.
In some countries new technological lines for the solution of this problem have been developed such as the use of absorbent materials such as the one described in U.S. Pat. No. 7,935,248, U.S. Pat. No. 7,094,333 and the references Denitrogenation of Transportation Fuels by Zeolites at Ambient Temperature and Pressure, Hernandez-Maldonado et al., Angewandte Chemie, 2004, pp. 1004-1006; Ultra-deep desulfurization and denitrogenation of diesel fuel by selective adsorption over three different adsorbents: A study on adsorptive selectivity and mechanism, Kim et al., Elsevier B.V., 2005, pp. 74-83; or through a process of oxidative denitrogenation (U.S. Pat. No. 7,666,297, U.S. Pat. No. 7,276,152).
Ionic liquids have been intensively studied in recent years due to its physico-chemical properties, such as: very low vapor pressure, they are not flammable, non-corrosive and low toxicity, they are excellent substitutes for common organic solvents (Wasserscheid, P.) Keim, W. (Eds.) Ionic Liquids in Synthesis, Wiley-VCH, Wenheim, 2004; Welton, T. Chem. Rev. 1999, 99, 2071-2084; Zhao, H.; Malhotra, S. V. Aldrichimica Acta 2002, 35, 75-83), which has promoted the rapid development of a wide variety of industrial applications for these compounds (Rogers, R. D.); Seddon, K. R. (Eds.) Ionic Liquids: Industrial Applications of Green Chemistry. ACS, Boston, 2002; Rogers, R. D.; Seddon, K. R. (Eds.) Ionic Liquids as Green Solvent: Progress and Prospects. (ACS Symposium Series), Boston, 2003; Rogers, R. D.; Seddon, K. R. (Eds.) Ionic Liquids IIIB: Fundamentals, Progress, Challenges and Opportunities: Transformations and Processes (ACS Symposium Series), Boston, 2005; Roger, R. D.; Seddon, K. R.; Volkov, S (Eds.). Green Industrial Applications of Ionic Liquids. (NATO Science Series), Kluwer Academic Publishers, Dordrecht, Netherlands, 2002.).
Ionic liquids are known for more than 30 years. Its heyday in different industrial applications started approximately 10 years ago (Rogers, R. D.;) Seddon, K. R. (Eds.), Ionic Liquids Industrial Applications of Green Chemistry, ACS, Boston, 2002). They are applied as solvents, as catalysts in alkylation, polymerization and Diels-Alder reactions, in electrochemical processes and as solvents for the extraction of CO2, sulphur and aromatic compounds from mixtures of hydrocarbons, among others. One of the first publications that mention the use of ionic liquids for removal of mercaptans in oils is WO 0234863, dated 2002 May 2. The patented method, is based on the use of sodium hydroxide in combination with Ionic liquids, to improve the conversion of mercaptans into mercaptides. Peter Wassercheid and collaborators, published from 2001 to 2005 several patents and articles on the topic of the use of ionic liquids, to the process of desulphurization in hydrocarbons (Chem. Comun. 2001, 2494, Green Chem. 2004 6, 316); WO 03037835, date of publication 2003 May 8; US 20050010076 A1, date of publication 2005 Jan. 13). In this work, the authors used liquids of the type C+A− where C+ is 1,3-dialkylimidazolium or tetra-alkylammonium, and A− are tetra-chloroaluminates or methanesulfonates. Through a process of repeated extractions (up to 8 successive extractions), high removal of sulfur compounds from gasoline model efficiencies were achieved.
U.S. Pat. No. 7,749,377, 2010, treats acidic ionic liquids containing the anion HSO4− for the selective removal of nitrogen compounds. However, no other patent has described the use of ionic liquids as proposed in the present invention for this application. Some authors have described this application in scientific papers using loads models, for example Eβer and collaborators found a good extraction efficiency of nitrogen compounds, using the Ionic [BMIM][OcSO4], for a sample model containing 1000 ppm of nitrogen as n-dodecane indole (Eβer, J., et. al.) Green Chem. 2004, 6, 316-322). Meanwhile Zhang and colleagues assessed the capacity of removal of nitrogen compounds with the Ionic Liquid [BMIM] BF4 using a model gasoline. Zhang, S. G., et al. Ind. Eng. Chem. Res. 2004, 43, 614-622. In the article by Li-Li Xie and collaborators (Green Chem., 2008, 10, 524-531) describes the selective extraction of neutral nitrogen compounds in diesel such as 1-butyl-3-methyl-imidazolium chloride using a model gasoline.